West Nile takes its toll on rare bird

July 20, 2004

West Nile virus has become a widespread human health concern, yet little attention is given to the grave situation facing certain wildlife species dying from the deadly disease, says a University of Alberta scientist. Cameron Aldridge is part of a research team to have shown that the West Nile Virus represents a significant new stressor on the sage-grouse–a species already on the endangered list in Canada and under current consideration for federal listing in the United States.

West Nile virus has become a widespread human health concern, yet little attention is given to the grave situation facing certain wildlife species dying from the deadly disease, says a University of Alberta scientist. Cameron Aldridge is part of a research team to have shown that the West Nile Virus represents a significant new stressor on the sage-grouse–a species already on the endangered list in Canada and under current consideration for federal listing in the United States.

”We don’t yet know whether the sage-grouse are more at risk than other species but we do know that the West Nile virus could have devastating consequences for small populations,” said Aldridge, a co-author on a research paper just published in ”Ecology Letters.”

Aldridge was part of a team that monitored radio-marked female sage-grouse from March 2003 to September 2004 in five sites in Alberta, Montana and Wyoming. They found that populations that had their first exposure to the virus in 2003, had a 25% decrease in late summer survival of females. West Nile virus was confirmed to have killed 18 individuals whose carcases could be relocated. Serum from 112 sage-grouse collected after the outbreak show that none had antibodies, suggesting that they lack resistance.

”When we tested individual sage grouse after the outbreak of the virus in 2003, we hoped we would find antibodies present for the virus, indicating some birds were infected, fought off the virus and survived, but we didn’t see that,” said Aldridge, a PhD candidate in the Faculty of Science. ”The immunity appears to be extremely low for sage-grouse, which means it is going to take much longer for the population to develop resistance to the virus and to survive, if they are indeed capable. We don’t know how long small populations like those found in Alberta or Saskatchewan can survive, while losing the genetic basis needed to maintain the population, but we may not have much time.”

The team’s findings suggest that large, healthy and highly productive populations that live in a high quality habitat don’t seem to be impacted as much as smaller less productive populations in poorer quality habitats–the habitat essentially ensures the population is productive, and more capable of buffering against catastrophic events. Trying to improve habitats that support robust, genetically diverse populations may be one way to try protect the bird, said Aldridge. Revisiting mosquito control programs may be another way to tackle the problem, but may only be a temporary band-aid solution.

When a species is placed on an endangered or threatened list it is often because it is already on the brink of disappearing and at that point it becomes crisis management and a fight to hang on to the species as long as possible, said Aldridge. ”We have a very limited understanding of West Nile virus and its implications for the persistence of many wildlife species. Right now, our best option to help those species to combat the virus, is to ensure that they have high quality habitats with few human impacts, to ensure that populations remain productive and robust to stochastic events.

”There is a fear of listing a species on the endangered list because it completely changes how industry will have to operate, so in a sense fear is good because everyone comes together to try to benefit the bird and its habitat.”